Two half-inch supply lines to same fixture

[Jefrf]

I was helping my neighbor replace a vanity in a bathroom and I sent him to shut off water to the sink. Everything he tried at the PEX manifold did not shut off the sink lines! Finally he closed two valves, one of which was not labeled, and it finally worked. Once I followed the to lines from the manifold to the crawl space under the bathroom, I found both lines ran parallel and joined up with "T" fittings to the same 1/2" PEX line that went to the sink, shower, and soaking tub. Why on Earth would there be two lines feeding the same room. I know the guy who used to live there did it and he's not the best DIY'er. Maybe he was just looking for more volume of water in case all fixtures were on at the same time and did not have any 3/4" pipe. It made for a heckuva time just turning off water to one thing.

Is this in any way ok? Or a complete hack? Should be re-run all of this with 3/4" from manifold to crawlspace, and "t" off with 1/2" for each separate fixture?

Thanks for any advice. Terrylove is my go to for plumbing advice.

 

[Reach4]

Better would be 3/4 for the hot to fill the extra-big tub, and 1/2 to the lavatory. Even better would be 3/8 to the lavatory hot.

 

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[Gsmith22]

that's a complete hack. 1/2 was installed originally and when flow was poor, they ran another 1/2 line teeing them together. 3/4 is better for a long run feeding multiple fixtures. Usually with a manifold, each 1/2" line only feeds one fixture. If it was me, I would tear it out and run a single 3/4 line to a multiport tee and then run individual 1/2 lines from the multiport tee to each fixture.

I think Reach4 meant "even better would be 3/4 to the lavatory hot."

 

[wwhitney]

No, he meant 3/8" to the lavatory hot (if dedicated). That's enough flow for a lavatory, and it reduces the wait time for hot water.

Fundamentally, there's nothing wrong with paralleling two 1/2" lines in lieu of a 3/4" line. I would say if it is working OK, just label the shutoff valves properly and call it a day.

Cheers, Wayne

 

[Gsmith22]

the internal area of two 1/2" pex pipes is still less than the internal area of one 3/4" pex pipe (albeit not by a lot) and the installation obviously ends up with more fittings too given the two pipes. its a shit show to put it politely. Will it work - sure it already has been working but its a service nightmare even if everything is labeled appropriately. Why? Because anyone coming in new to the situation won't understand the layout (or believe the homeowner's explanation of the layout) because NO ONE does this. I'm not suggesting it has to come out today because of some safety issue but it would get put on the "to do" list at my house.

 

[wwhitney]

the internal area of two 1/2" pex pipes is still less than the internal area of one 3/4" pex pipe (albeit not by a lot) and the installation obviously ends up with more fittings too given the two pipes.

Actually, on the area, (2) 1/2" PEX pipes comes out every so slightly ahead, so it's more or less equal. PEX pipes are SDR9, so the internal area ratio is just the square of the external diameter ratio. For 3/4" pipe compared to 1/2" pipe, that's (7/5)^2 = 49/25 = 1.96.

Agreed, on the extra fitting, but's just one tee.

To me, it's an unusual quirk, and not how you'd do things in a new design, but a not unreasonable choice in a retrofit situation, once properly labeled. If it bugs you, by all means go ahead and replace it.

Cheers, Wayne

 

[Jadnashua]

It allowed them to maybe make that run without going out and buying some 3/4" stuff and maybe need a new manifold and fittings.

 

[Jeff H Young]

It allowed them to maybe make that run without going out and buying some 3/4" stuff and maybe need a new manifold and fittings.

Thats a possibilty. Kinda sloppy but could be reason for it .

 

[Jason Bradshaw]

I am a little late on this thread, I came across it when searching for something else. Could the original reason for the second line actually been for a water circulation pump that was never installed?